Salts of various compounds containing acid moieties, including ionomeric polymers, are known to be hydrophilic and have been used in a variety of applications where increased fluid absorbency is desirable, typically as super absorbent powders. Superabsorbent powders have been used to increase the absorbency of diapers, wipes, and cable wrapping strips for high voltage electrical cables, to name but a few uses for these compounds. For example, Buchwald et al. U.S. Pat. No. 4,820,560 discloses that a cross linked sodium salt of a polyacrylic acid serves as a super absorbent swellable powder for use in cable wrapping strips for high voltage electrical lines. The cable wrap is a nonwoven fabric containing the superabsorbent powder and swells upon exposure to moisture to seal the cable core from water and prevent the propagation of water lengthwise of the cable. Gross U.S. Pat. No. 3,966,679 discloses that cross linked salts of polymers containing carboxylic acid groups are useful as water swellable absorbent particles for incorporation in surgical sponges, diapers, tampons, meat trays, bath mats, and the like products.
Superabsorbent powders can be somewhat costly to prepare and their incorporation into fabrics and other articles for providing increased absorbency normally adds manufacturing and fabricating steps, increasing the cost of providing the fabric or article. Problems have also been encountered in keeping the powder fixed in the fabric or other article until use.
Another method for using hydrophilic compounds in fabrics and other articles that avoids some of the complications of powders is to form fibers and fibrous structures from fiber forming compositions that contain one or more hydrophilic compounds. For example, salts of acid containing copolymers, including ionomers, have been incorporated into the polymer resins from which fibers and various fibrous structures have been made, thus avoiding some of the problems associated with using superabsorbent powders. Bohme U.S. Pat. No. 3,801,551 discloses that acid polymers including salts of acid polymers may be converted to fibrillar masses by digesting structured solid granules of the compounds in aqueous alkaline media and applying shear forces by intensive stirring to convert the granules to fibrillar masses. The fibrillar masses are disclosed to be useful for mixing with other fibrous materials to make felted articles, paper-like products, filters, and the like, and for shaping into cups and other articles.
Le-Khac U.S. Pat. No. 4,731.,067 discloses dry spinning of fibers from copolymers including some ionomers to produce water-.absorbing compositions. The copolymers described by Le-Khac are blended with from about one to ten percent by weight (blended weight) of at least one monomer having a molecular weight less than 1000 and containing at least two hydroxyl groups. The monomer is said to serve as a cross linking agent for the copolymer, which results in the formation of covalent bonds upon curing at elevated temperatures of from, for example, 140.degree. C. or higher to 200.degree. C. or higher, depending upon the copolymer.
Dry spinning is characterized by extruding a solution of a fiber.-forming substance dissolved in a suitable solvent in a continuous stream and into a heated chamber to remove the solvent, leaving the solid filament, as is commonly used in the manufacture of acetate. Le-Khac U.S. Pat. No. 4,731,067 exemplifies a dry spinning method wherein fibers are spun from an aqueous solution of polymer and the water is then evaporated. Dry spinning sometimes is referred to in the technical literature as solvent spinning.
Dry spinning is distinguished from other methods of producing synthetic fibers, such as melt spinning. In melt spinning a molten fiber is extruded from a molten fiber forming substance through a die or spinneret in the absence of a solvent and at a constant rate under high pressure. The liquid polymer streams merge downward from the face of this spinneret, into air or other gas or into a suitable liquid. The polymer streams solidify and typically are used to form either meltblown or spunbonded webs, as described below, or drawn or attenuated mechanically after solidification using Godet rolls and are brought together to form threads and wound up on bobbins. In comparison to melt spinning, dry spinning is a more complicated, time consuming, and costly procedure and requires more careful treatment of the fibers produced therefrom.
Meltblowing, in particular, is an economical method for producing nonwoven products. In melt blowing, the extruded molten fibers are attenuated and then broken with a hot, high velocity air stream or steam to produce short fiber lengths. The short fibers are collected on a moving screen where they bond during cooling. Meltblowing is discussed in patent literature, e.g. Buntin, et al. U.S. Pat. No. 3,978.185; Buntin U.S. Pat. No. 3,972,759; and McAmish et al. U.S. Pat. No. 4,622,259. These patent disclosures are hereby incorporated by reference.
To form a spunbonded web, a molten polymer is extruded through a spinneret to form a multiplicity of continuous filaments, and the filaments of molten polymer are solidified and then drawn or attenuated, typically by a high velocity fluid, and then randomly deposited on a collection surface, such as a moving belt, to form a web. The filaments are then bonded to give the web coherency and strength.
European Patent Application Publication No. 0 351 318 describes meltblowing polymeric dispersions of incompatible thermoplastic resins, some of which include ionomers. The various polymeric dispersions include blends of polypropylene with ionomers that are sodium and calcium salts of copolymers of acrylic acid and ethylene. One thermoplastic resin forms a continuous phase, and one forms microfibrils dispersed as a separate phase. The multi-component fiber can be used to prepare nonwoven webs, or the continuous phase can be dissolved to yield microfibrils that can be made into various products. The webs and microfibrils may be used as wipes, napkins and personal care items; absorbents for drugs, urine, and similar fluids; for release of bactericides, drugs, fungicides, and insecticides; as filters, ionic exchange resins, and battery separators.
Although blends of ionomers with polyolefins, monomers, or other cross linking agents or incompatible polymers have been used to produce fibers and nonwoven webs, ionomers in the unblended state have not been used to produce fibers and nonwoven webs. Blending the ionomers with polyolefins, monomers, or other cross linking agents or incompatible polymers introduces complexity into the fiber spinning process and limits the properties available in fibers and webs produced from the blends.